controlled by traditional interests with little concern for accelerating the processes of modernization. Political Effects of Differential Population Growth Rates within a Country Within virtually all societies, some groups increase their numbers more rapidly than others. Mortality rates, especially infant mortality rates and fertility rates, vary markedly from one socioeconomic class to another, from one ethnic group to another, and from one geographic region to another. Insofar as numbers constitute an element in the political power of social groups, we can say that differential population growth rates affect the distribution of political power within a society. Size and Power. How important is the size of a social group as a determinant of its political power? This is not the place to suggest a theory of power which would indicate the precise importance of numbers, say in relation to the cohesiveness and organizability of a social group, its skill, and financial resources, or its ability to deny goods and services to others. Moreover, the "mix" of such variables depends upon the kind of political system in which the social group operates—whether it is democratic or not, the kind of system of representation it has, or how important elections are in the political system. For our purpose it is sufficient to note first that the size of a particular social group, and particularly of an observable ethnic group, is a factor in its political power, particularly in democratic systems. And second, in many political systems, different ethnic groups, socioeconomic classes, and geographic groups often perceive differences in size and growth rates as factors affecting the distribution of power. A few examples should suffice to demonstrate how changing population growth rates or perceptions of changing growth rates affect the distribution of power within political systems and affect the relationships among social groups.* Much of the support for family planning programs in Britain in the latter part of the 19th century occurred at a time when there were sharp disparities in fertility rates between upper and middle class Englishmen and the working class. Among each group of 100 women in the upper and middle classes married between 1881 and 1886, there had been born 422 children. In contrast, for each 100 women in the unskilled laboring class there had been bom 609 children, and among miners' wives 684 children had been born. In other *The literature on differences in fertility, both within and between nations, is extensive. For a list of some recent significant studies, see Heer (44, pp. 48-53). Heer discusses the controversial literature concerning the inverse relationship between income and fertility, differential fertility rates between Protestants and Catholics, and differential fertility rates between blacks and whites. Though there is a substantial literature on differential fertility rates, less has been written on its social and political consequences.ion, for example, as a result of the dense concentration of automobiles. The cconomies-of-scale argument, therefore, cuts both ways. less important.